1. Field of the Invention
The present invention relates to a hydraulic pressure control device for an automatic transmission for a vehicle such as an automobile, and more particularly, to a hydraulic control device equipped with a reverse inhibition mechanism for inhibiting that a reverse stage is set up by malfunction of the hydraulic control device.
2. Description of the Prior Art
In the art of automatic transmission for a vehicle such as an automobile it has already been proposed as described in, for example, Japanese Patent Laying-open Publication 60-37446 to incorporate a reverse inhibition mechanism in a hydraulic control device for the automatic transmission so as to inhibit that the reverse stage is set up by an erroneous manual shifting of a manual shift valve to a reverse range by the driver during forward running of the vehicle.
Such a reverse stage inhibition mechanism has a reverse stage inhibition valve generally called a reverse inhibition valve for selectively communicating or interrupting a hydraulic pressure supply passage for a hydraulic pressure chamber of a friction engaging means for setting up the reverse stage. Such a reverse inhibition valve has a valve element movable between a permission position for communicating said hydraulic pressure supply passage and an inhibition position for interrupting said hydraulic pressure supply passage, said valve element being adapted to be driven by a hydraulic pressure supplied to an inhibition port thereof so as to inhibit the setting up of the reverse stage.
Further, in order to prevent that said valve element moves to said inhibition position by an erroneous operation when once the setting up of the reverse stage has been allowed, it is contemplated to hold said valve element at said permission position, as proposed in patent application Ser. No. 07/302,256 assigned to the same assignee as that of the present application.
When the friction engaging means supplied with a hydraulic pressure for setting up the reverse stage is also supplied with a hydraulic pressure for setting up a forward speed stage such as the first speed stage, if in a speed stage shifting from the first speed stage to the reverse stage by operation of a manual shift valve the exhausting of the hydraulic pressure from the friction engaging means delays, the valve element for controlling allowance and inhibition of the reverse stage will be held at its allowance position by the hydraulic pressure for the first speed stage even when the reverse inhibition operation is to be obtained.